Measuring device



Dec. 25, 1956 z, w. WILCHINSKY MEASURING DEVICE Filed Sept. 27, 1946 MEASU RED MEASURED TO SlGNAL TO BE TO BE TO SIGNAL INVENTOR. ZIGMOND W. WILCHINSKY BY W ATTORNEY United States Patent" MEASURING DEVICE Zigmond W. Wilchinsky, Baton Rouge, La. Application September 27, 1946, Serial No. 699,650

3 Claims. (Cl. 250-27) (Granted under Title 35, U. S. Code (1952), see. 266) This invention relates to electrical signal measuring devices and in particular to devices for measuring high frequency voltages.

Frequently it is desirable to measure alternating voltages existing between conductors of a coaxial transmission line. Where the frequency of the alternating voltages is high, conventional measuring methods are generally undesirable. Typically, where diode peak detectors are employed it is necessary to strike a compromise between electrode spacing within the diode and rectification efliciency. At high frequencies electron transit time must be kept small. In conventional diodes this is only possible by maintaining close spacing between electrodes. Close electrode spacing on the other hand is not desired because of increased capacity and danger of dielectric breakdown between elements which tends to limit the voltage which can be handled.

It is, therefore, an object of the present invention to provide a voltage measuring device by which voltage measurements are obtained without compromising between transit time and voltage handling capability.

Another object of the present invention is to provide a voltage measuring device in which electrons are subjected to accelerating and decelerating fields to minimize transit time difficulties with distant electrode spacing.

Other and further objects and features of the present invention will become apparent upon a careful consideration of the accompanying drawings and following detailed description of a typical embodiment of the invention.

Fig. 1 shows a preferred embodiment of the features of the present invention as employed in conjunction with a coaxial electrical assembly.

Fig. 2 is a variant embodiment of the present invention.

In accordance with the general concept of the present invention, a voltage measuring device is provided in which electron transit time is held to a low value despite large electrode spacing. To reduce transit time and yet maintain high breakdown voltage an electron discharge system is employed in which the electrons are subjected to an accelerating field before being admitted into a space across which the alternating voltage to be measured is maintained. These accelerated electrons are then further accelerated by the action of the alternating fields existing in the space. Finally, the accelerated electrons are permitted to leave the fieldsof influence of the accelerating potentials and are decelerated to a condition of substantially zero velocity. The accelerating and decelerating potentials as employed are preferably of a D. C. nature and hence are easily measurable by conventional equipment. The magnitude of the alternating voltage transmitted through the device is then readily determined because the sum of the accelerating voltages must be equal to the decelerating potential.

With particular reference to Fig. 1, a coaxial assembly having inner and outer conductrs '10 and 11, respectively, is shown. Inner conductor is supported within conductor 11 by insulating spacer washers 12 and 13. Inner conductor 10 is further provided with an axially drilled ice hole indicated by numeral 14 into which an electron source 15 is inserted. Electron source 15 may be of any conventional electron tube variety such as a coated wire resistively heated by the passage of an electric current supplied to terminals 16 and 17. Electron source 15 is supported within conductor 10 byan insulating washer 18. Conductor 10 is circumferentially perforated over a central portion of the section between washers 12 and 13, the apertures being indicated in general by numeral 19. Outer conductor 11 is also circumferentially perforated in the region thereof between washers 12 and 13, the openings being indicated in general by numeral 20. The perforated portion of conductor 11 is enclosed by a pair of annular insulating discs 21, 22 and a cylindrical section 23 of conductive material. The inner structure as defined by conductor 10, washers 12, 13, washers 21, 22 and cylinder 23 is hermetically sealed and evacuated, said evacuation being made by means of a suitable connector 24 to a source of vacuum, not shown. Suitable voltage apparatus is provided for supplying an accelerating potential between conductor 10 and electron source 15 as well as a decelerating potential between conductor 11 and cylinder 23, and for measuring current flow to cylinder 23.

In operation, the electron source 15 is placed at a known D. C. potential made negative with respect to the inner conductor 10 by battery 15A. Thus, electrons leaving source 15 will travel outwardly in a radial direction achieving considerable velocity because of the potential difference between the source 15 and the conductor 10. Some of the electrons, of course, will impinge upon conductor 10 and be lost, while other electrons will pass through aperture 19 into the space between conductors 10 and 11. In the portion of the alternating current cycle in which conductor 11 is positive with respect to the conductor 10, the electrons Within the space therebetween will be further accelerated achieving a high velocity by the time they reach the surface of conductor 11. Again some of these electrons will be lost when they fiall upon the positive conductor 11. However, some electrons will continue through apertures 20 into the space between conductor 11 and cylinder 23. These electrons traveling with considerable velocity in the direction of cylinder 23 would normally come to rest on cylinder 23. To prevent this action, cylinder 23 is provided with suitable potential negative with respect to conductor 11 from potential source 25. This negative potential exerts aretarding force on the electrons and if the magnitude thereof is sufficient the velocity of the electrons moving toward cylinder 23 will be reduced to zero so that no electrons will actually impinge upon cylinder 23. This state may be detected by observing a zero reading on ammeter 25B. From here on it is unimportant what actually happens to the electrons. In all probability they will drift back to conductor 11 and be collected thereby.

The final velocity achieved by an electron subjected to the action of several accelerating or decelerating fields is directly proportional to the magnitude of the accelerating or decelerating voltages. Thus, the decelerating voltage applied between cylinder 23 and conductor 11 must be equal to the maximum instantaneous sum of the alternating voltage applied between conductor 10 and 11 and the initial accelerating potential applied between source 15 and conductor 10. Such a condition, of course assumes negligible velocity of electrons when they are initially emitted by source 15. If desired, the voltmeter 25A may be provided with a scale giving direct reading of the difference between the voltage applied between conductor 11 and cylinder 23 and between source 15 and conductor 10.

With reference now to Fig. 2, a variant embodiment of the basic device is shown in which an electron emitting'source 26 is placed external to inner conductor 27 eliminating the requirement of sending a heater current through the inner conductor. Electron emitting source 26 is placed at a known D. C. potential made negative with respect .to the outer conductor 31 byv a battery such as 15A. The battery would be connected between conductor 28 and outer conductor 31. Heater power for electron source 26 is supplied through terminals 28 and 28A which are connected to the source 26 through insulating sleeves 29 and 30. Outer conductor 31 is provided with a group of openings indicated in general by numeral 32 through which electrons from source 26 may pass to enter the space between conductors 27' and 31. As before, an accelerating potential is placed between electron source 26 and conductor 31 so that electrons from source 26 are accelerated to a high velocity before being admitted into the space between conductors 31 and 27. As shown, an electron director shield 26A is provided with a negative potential with respect to the source 26 to direct electrons toward the apertures 32.

The central portion of inner conductor 27 is provided with a rectangular shaped opening through which electrons from source 26 may pass. Diametrically opposite apertures 32, a second set of apertures 34 is arranged to receive the electrons delivered into the space between conductors 27 and 31. Located external to the conductor 31 beyond apertures 34 is a collector plate35 to which is supplied a negative potential through terminal 36 to exert a decelerating force upon the electrons. Thus electrons leaving source 26 are initially accelerated by the potential difference between the source 26 and the outer conductor 31 into the vicinity of apertures 32. Electrons passing through apertures 32 into a first space between conductors 31 and 27 are accelerated toward conductor 27 during the portion of the alternating wave having the proper polarity. A portion of these electrons are collected on conductor 27; however, some electrons find their way through the rectangular opening 33 and into a second space inner conductor 27 and outer conductor 31 in the opposite portion of the assembly. Again if proper reversal in the phase of the alternating wave has taken place the electrons will be further accelerated Electrons passing toward the outer conductor 31. through apertures 34'toward collector. plate 35 are then decelerated by the negative potential mentioned. above which is adjusted to a point at which electrons are repelled and do not strike plate 35. It is to be understood that the negative potential applied to plate 35 is applied through the use of the same arrangement as was used with reference to cylinder 23. That is a suitable negative potential is obtained from the adjustable potential source 25. Further an ammeter 25B may be provided to give by direct reading, notice when the threshold condition has been achieved. This condition is achieved when the vlotage applied between collector 35 and conductor 31 is equal to the voltage applied between source 26 and conductor 31 plus twice the peak alternating voltage existing between conductors 27 and 31. This voltage may be read on voltmeter 25A. As before these electrons find their way back to the outer conductor 31 in the vicinity of apertures 34.

In this case it is to be seen that it is necessary to have the proper relationship between transit time through each side of central conductor 27 and the duration of the half cycle of the alternating energy to be measured. Such a condition would, of course, be optimum at a certain frequency or in a certain frequency band. This device is, therefore, frequency selective operating best only for selected frequency. Considerable range of operating frequencies may be accommodated however,

simply by variation in the potential between the elecly equal to the sum of the initial accelerating potential between source 26 and conductor 31 plus twice the peak A. C. voltage existing between conductors 27 and 31 and may be measured as before with a voltmeter having suitable altered scale connected between plate 35 and conductor 31.

From the foregoing discussion it is apparent that considerable modification of the features of this invention is possible and while the devices here shown and the apparatus for the operation thereof constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise devices and forms of apparatus and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. Apparatus for measuring the peak amplitude of an alternating wave, comprising; a coaxial assembly having perforated portions of inner and outer conductors thereof, insulating spacers supporting the inner conductor within the outer conductor, an electron source located withinthe inner perforated conductor, a collector plate located external to the perforated portion of the outer conductor, means maintaining the electron source at a negative potential with respect to the inner conductor, and means applying a decelerating potential between the collector plate and the outer conductor of sufiicient magnitude to prevent electron flow and the electron source to the collector plate.

2. Apparatus for determining peak amplitude of an alternating .wave, comprising; a coaxial assembly having perforated portions of inner and outer conductors thereof, insulating spacers supporting the inner conductor within the outer conductor, a source of electrons located in an enclosed. space external to the outer conductor, means maintaining the electron source at a negative potential with respect to the outer conductor, an electron collector. plate located in a second enclosed space external tothe outer conductor diametrically opposite the electron source, a shield partially enclosing the electron source to direct the electron flow toward the collector plate, and means applying a decelerating potential of sufiicient magnitude to the collector plate to prevent electron flow thereto.

3. An apparatus for measuring peak amplitude of an alternating electrical wave comprising, a coaxial assembly having perforated portions of innerand outer conductors thereof, insulating spacers supporting the inner con-. ductor within the outer conductor, enclosing means attached to'said outer conductor surrounding the perfo-.

rated portions thereof for providing, with saidinsulating spacers, an evacuable area enclosing said perforated portions, a source of electrons within said evacuable area, an electron collector plate external to said outer conductor but within said enclosing means, means maintaining said electron source at a negative potential with respect to the closest of said conductors, and means applying an electron decelerating potential to said collector plate of sufficient magnitude to prevent electron flow from said electron source to said plate.

References Cited in the file of this patent UNITED STATES PATENTS 1,982,271 Turner Nov. 27, 1934 2,259,690 Hansen et al Oct. 21, 1941' 2,287,845 Varian et al June v30, 1942 2,337,124 Tunick Dec. 21, 1943 2,368,031 Llewellyn Jan. 23, 1945 2,472,038 Yando May 31, 1949 2,488,420 Ludwig Nov. 15, 1949 

